1. Field of the Invention
The invention relates to a process for oxidizing an article, especially a process for the oxidation coating of a surface of a metal or a semiconductor material. The invention furthermore relates to a process for removal of oxidation from articles, such as dry precision cleaning or the like.
More specifically, the invention relates to a process for the removal of impurities of organic compounds which have accumulated on a surface of a metal or a glass plate as well as to a process for elimination of unnecessary photoresist on a silicon wafer in a production process for a semiconductor device.
2. Description of Related Art
Recently a treatment technique was developed and introduced into practice, in which the interaction of ultraviolet light with ozone is used in a process for removing organic impurities which have accumulated on a surface of a metal, glass or the like without damaging the articles being treated, and in a process for formatting an oxide layer on the pertinent surface.
A technique of this type is described for example in the handbook "New Technology for Ozone Use" (San Yu Shobo Verlag. Nov. 20, 1986, Chapter 9, p. 301 to 313; hereinafter called "Document A") including the principle underlying it, its devices, its cleaning effect, its applications and the like.
It can be taken from this publication that when oxygen or oxygen-containing air is radiated with light of 185 nm wavelength, which is emitted by as a vacuum ultraviolet ray from a mercury low pressure lamp, ozone is generated with it. In this case, furthermore, some of the ozone generated is decomposed by light of a 254 nm wavelength (which is a far ultraviolet ray emitted from the same mercury low pressure lamp), into an activated oxygen which is a decomposed gas of ozone, and the activated oxygen is brought into contact with the surface of the articles to be treated.
Removal of the organic impurities is done such that the organic impurities which have adhered to the surface of the articles to be treated, due to the above-described contact, are oxidized and changed into a low molecular oxide, such as carbon dioxide, water or the like. The low molecular oxide is removed from the surface of the articles to be treated, so that dry precision cleaning of the surface of the above-described articles to be treated can be performed.
Another process is performed such that ozone generated by an ozonizer is introduced directly into a treatment chamber, instead of generating ozone with 185 nm wavelength light, where it is irradiated and decomposed with 254 nm wavelength light (which is a far ultraviolet ray emitted from the mercury low pressure mercury lamp) to produce activated oxygen. The ozone and the activated oxygen are brought into contact with the surface of the articles to be treated, so that oxidation removal of the organic impurities on the above-described surface is obtained.
In the technique described in Document A, however, it is regarded as disadvantageous that, in the case when the ozonizer is not used, the ozone concentration decreases and that, therefore, to increase an absolute amount of ozone to be produced, a value (d.times.p) which is determined by a distance d (cm) of one passage of the ray with 185 nm wavelength and an oxygen partial pressure p (air pressure) had to be greater than/equal to a certain value. Specifically, at an oxygen partial pressure p of 0.2 atm., air pressure at a distance d of greater than or equal to 10 cm is necessary. This means that it ordinarily was, in fact, necessary that the value (d.times.p) be greater than 2. The technique described above, therefore, had the disadvantages that a large device was needed and that, at the same time, the treatment speed for oxidation removal of the organic impurities or the like is low because a high concentration of ozone cannot be obtained. Furthermore, it is regarded as disadvantageous that the conditions of use of the ozonizer were limited by the fact that it is inherently costly and thus causes financial problems.
The technique which uses the interaction of ultraviolet rays and ozone is, on the other hand, also used for a device for removing unnecessary photoresist on a silicon wafer, which is called a "photo asher". In this case, two processes, i.e., with and without use of the ozonizer, can be executed. However, in order to quickly remove a photoresist with a conventional thickness of, for example, roughly 1 micron, ultimately, it is, necessary to use the low pressure mercury lamp together with the ozonizer. Therefore, reference should, be made to the above-noted disadvantages of an expensive device, the high cost in the treatment process, and a large installation area and the like.